A heat exchange tube is already known, as disclosed in, for example, Japanese Patent Application Laid-open No. 2004-85142. The heat exchange tube disclosed in Japanese Patent Application Laid-open No. 2004-85142 will be described based on FIGS. 7 to 9.
There is a conventional heat exchange tube 014 in which a plurality of projecting portions 031 are arranged in a zigzag form along an axis of the tube as shown in FIG. 7. In this case, there are the projecting portions 031 as shown in FIG. 8 and FIG. 9. In FIG. 8, the projecting portion 031 is formed so that its ridge becomes linear, and a peripheral wall 030 of the portion other than the projecting portion 031 is not deformed. In FIG. 9, the projecting portion 031 is also formed so that the ridge becomes linear, but the peripheral wall of the portion other than the projecting portion 031 is deformed so that opposite end portions in the peripheral direction of the projecting portion 031 are protruded.
Incidentally, the projecting portion shown in FIG. 8 is unfavorable in workability since the thickness of the ridge portion of the projecting portion 031 inevitably increases more than the thickness of it before formation of the projecting portion, and due to the linear ridge of the projecting portion 031, the peripheral length of the tube in the projecting portion 031 decreases more than that before formation of the projecting portion, and sufficient increase in the surface areas of the inside and outside of the tube cannot be desired due to the projecting portion. Further, in the projecting portion shown in FIG. 9, increase in the plate thickness of the ridge portion of the projecting portion 031 can be suppressed, but protruded portions 031a are formed at opposite ends in the peripheral direction of the projecting portion 031. Therefore, when the tube is inserted into the hole of another member, the protruded portions 031a inhibit or interfere with insertion of the tube, and have an adverse effect on the assembly property.
Further, as shown in FIG. 7, the height of each of the projecting portions 031 is set to be lower than the radius of the tube 014, and therefore, a linear main flow path F with which a plurality of projecting portions 031 do not interfere is formed inside the tube 014, which makes agitation of a fluid inside the tube 014 difficult, and inhibits enhancement of efficiency of heat exchange.